Distribution of High-Magnesium Calcite in Lime Muds of the Great Bahama Bank: Diagenetic Implications

Abstract

ABSTRACT Studies of Pleistocene low-magnesium calcite analogs of Recent carbonate sediments indicate that the initial distribution of high-magnesium calcite in aragonitic sediments may play a critical role in the preservation of sedimentary texture and fabric during freshwater diagenesis. Thus the distribution of high-magnesium calcite in Recent sediments provides a basis for speculation concerning potential diagenetic fabrics in analogous materials from older stratigraphic sequences. That portion of the Great Bahama Bank which lies to the west of Andros Island is commonly cited as a vast area of accumulation of aragonitic sediments. The objective of this study was to estimate the amount and distribution of calcite within the various sediment types of this area. It is concluded that significant amounts of high-magneisum calcite are ubiquitous in the sediments. Furthermore, the so called aragonite needle lime of this area are shown in fact to be richer in high-magnesium calcite than their associated coarse sediment fractions. The abundance of calcite nuclei in ancient lime muds is suggested to be a significant factor leading to the preservation of the texture of such sediments. It is unlikely that loss of mass or textural obliteration in muddy carbonates in the stratigraphic record can be ascribed to the absence of original calcite nuclei in sediments from environments similar to that of the modern Great Bahama Bank.